Android NullPointerException CipherInputStream to Bitmap

Question

I'm tryin to get encrypted files from assets folder,decrypt it in application and show it as a content in list view.I'm using a well known Fedor's Lazy List Loading implementation.As you can see, I changed his getBitmap method with my own method :

package com.custom.lazylist;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.Stack;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import com.fedorvlasov.lazylist.R;
import android.app.Activity;
import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.widget.ImageView;

public class ImageLoader extends Activity {

    //the simplest in-memory cache implementation. This should be replaced with something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
    private HashMap<String, Bitmap> cache=new HashMap<String, Bitmap>();

    private File cacheDir;

    public ImageLoader(Context context){
        //Make the background thead low priority. This way it will not affect the UI performance
        photoLoaderThread.setPriority(Thread.NORM_PRIORITY-1);

        //Find the dir to save cached images
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"LazyList");
        else
            cacheDir=context.getCacheDir();
        if(!cacheDir.exists())
            cacheDir.mkdirs();
    }

    final int stub_id=R.drawable.stub;
    public void DisplayImage(String url, Activity activity, ImageView imageView)
    {
        if(cache.containsKey(url))
            imageView.setImageBitmap(cache.get(url));
        else
        {
            queuePhoto(url, activity, imageView);
            imageView.setImageResource(stub_id);
        }    
    }

    private void queuePhoto(String url, Activity activity, ImageView imageView)
    {
        //This ImageView may be used for other images before. So there may be some old tasks in the queue. We need to discard them. 
        photosQueue.Clean(imageView);
        PhotoToLoad p=new PhotoToLoad(url, imageView);
        synchronized(photosQueue.photosToLoad){
            photosQueue.photosToLoad.push(p);
            photosQueue.photosToLoad.notifyAll();
        }

        //start thread if it's not started yet
        if(photoLoaderThread.getState()==Thread.State.NEW)
            photoLoaderThread.start();
    }


    //MY METHOD
private Bitmap getBitmap(String src) {
    Bitmap myBitmap = null;
        //Decryption
        try {
        Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
        SecretKeySpec keySpec = new SecretKeySpec("01234567890abcde".getBytes(), "AES");
        IvParameterSpec ivSpec = new IvParameterSpec("fedcba9876543210".getBytes());
        cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);

        AssetManager is = this.getAssets();        
        InputStream input = is.open(src); //open file in asset manager
        CipherInputStream cis = new CipherInputStream(input, cipher);

        myBitmap = BitmapFactory.decodeStream(cis);

        }
        catch(Exception e){
            e.printStackTrace();
            Log.v("ERROR","Error : "+e);
        }


        return myBitmap;
    }



    //Task for the queue
    private class PhotoToLoad
    {
        public String url;
        public ImageView imageView;
        public PhotoToLoad(String u, ImageView i){
            url=u; 
            imageView=i;
        }
    }

    PhotosQueue photosQueue=new PhotosQueue();

    public void stopThread()
    {
        photoLoaderThread.interrupt();
    }

    //stores list of photos to download
    class PhotosQueue
    {
        private Stack<PhotoToLoad> photosToLoad=new Stack<PhotoToLoad>();

        //removes all instances of this ImageView
        public void Clean(ImageView image)
        {
            for(int j=0 ;j<photosToLoad.size();){
                if(photosToLoad.get(j).imageView==image)
                    photosToLoad.remove(j);
                else
                    ++j;
            }
        }
    }

    class PhotosLoader extends Thread {
        public void run() {
            try {
                while(true)
                {
                    //thread waits until there are any images to load in the queue
                    if(photosQueue.photosToLoad.size()==0)
                        synchronized(photosQueue.photosToLoad){
                            photosQueue.photosToLoad.wait();
                        }
                    if(photosQueue.photosToLoad.size()!=0)
                    {
                        PhotoToLoad photoToLoad;
                        synchronized(photosQueue.photosToLoad){
                            photoToLoad=photosQueue.photosToLoad.pop();
                        }
                        Bitmap bmp=getBitmap(photoToLoad.url);
                        cache.put(photoToLoad.url, bmp);
                        Object tag=photoToLoad.imageView.getTag();
                        if(tag!=null && ((String)tag).equals(photoToLoad.url)){
                            BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);
                            Activity a=(Activity)photoToLoad.imageView.getContext();
                            a.runOnUiThread(bd);
                        }
                    }
                    if(Thread.interrupted())
                        break;
                }
            } catch (InterruptedException e) {
                //allow thread to exit
            }
        }
    }

    PhotosLoader photoLoaderThread=new PhotosLoader();

    //Used to display bitmap in the UI thread
    class BitmapDisplayer implements Runnable
    {
        Bitmap bitmap;
        ImageView imageView;
        public BitmapDisplayer(Bitmap b, ImageView i){bitmap=b;imageView=i;}
        public void run()
        {
            if(bitmap!=null)
                imageView.setImageBitmap(bitmap);
            else
                imageView.setImageResource(stub_id);
        }
    }

    public void clearCache() {
        //clear memory cache
        cache.clear();

        //clear SD cache
        File[] files=cacheDir.listFiles();
        for(File f:files)
            f.delete();
    }  

}

.....but the problem is that I'm getting this Exception :

08-11 11:11:45.293: WARN/System.err(1073): java.lang.NullPointerException
08-11 11:11:45.293: WARN/System.err(1073):     at android.content.ContextWrapper.getAssets(ContextWrapper.java:74)
08-11 11:11:45.293: WARN/System.err(1073):     at com.custom.lazylist.ImageLoader.getBitmap(ImageLoader.java:79)
08-11 11:11:45.293: WARN/System.err(1073):     at com.custom.lazylist.ImageLoader.access$0(ImageLoader.java:70)
08-11 11:11:45.293: WARN/System.err(1073):     at com.custom.lazylist.ImageLoader$PhotosLoader.run(ImageLoader.java:200)

this is how I use LazyAdapter in my main class :

 public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        list=(ListView)findViewById(R.id.list);
        adapter=new LazyAdapter(this, mStrings);
        list.setAdapter(adapter);

        list.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> a, View v, int position, long id) 
            {
                Intent i = new Intent(v.getContext(), Cards.class);
                startActivity(i);

            }
        });

        Button btn = (Button) findViewById(R.id.btn);
        btn.setOnClickListener(listener);

/*          adapter.imageLoader.clearCache();
            adapter.notifyDataSetChanged();*/

        }

    @Override
    public void onDestroy()
    {
        adapter.imageLoader.stopThread();
        list.setAdapter(null);
        super.onDestroy();
    }



    public OnClickListener listener=new OnClickListener(){
        @Override
        public void onClick(View arg0) {
            adapter.imageLoader.clearCache();
            adapter.notifyDataSetChanged();
        }
    };

    private String[] mStrings={
            "card1_encrypted.jpg",
            "card1_encrypted.jpg",
            "card2_encrypted.jpg",
            "card1_encrypted.jpg",
            "card3_encrypted.jpg",
            "card1_encrypted.jpg",
            "card1_encrypted.jpg",
            "card3_encrypted.jpg",
            "card3_encrypted.jpg",
            "card2_encrypted.jpg",
            "card4_encrypted.jpg",
            "card5_encrypted.jpg",
            "card3_encrypted.jpg",
            "card2_encrypted.jpg",
            "card5_encrypted.jpg",
            "card1_encrypted.jpg"

    };

So any ideas how to fix that?An last thing: at line 79 I have this:

AssetManager is = this.getAssets();

Thanks in advance!

WHere is the onCreate() method? Your class extends Activity but your constructor doesn't super Activity's onCreate(). — , Aug 11 '11 at 11:28
There is no main class. You need something like this: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); — , Aug 11 '11 at 11:32
Damn,I just realize that...but when I remove extends Activity I got an error : "The method getAssets() is undefined for the type ImageLoader" — hardartcore, Aug 11 '11 at 11:32
If I remove my construcor, I got errors in other files.Because basically I use this ImageLoader class only for loading the image in Lazy Adapter class,where I set the data for list view. I just need to know is that the right way to get files from assets,and how to return the decrypted image. — hardartcore, Aug 11 '11 at 11:40
Then dont extend Activity. In your constructor you need an AssetManager argument. When this class is called from an Activity, you need to use that activity's AssetManager instance as the argument. — , Aug 11 '11 at 11:42

score 0 · Answer 1 · 2011-08-11T13:00:33.127

0

You need an onCreate() method.

  @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        AssetManager am = getAssets();//this should not get a nullpointerexception
  }

Or do the following:

In your Activity (whichever one calls image loader) write this:

ImageLoader il = new ImageLoader(this);//this being the context.

Then in your ImageLoader class you can use

AssetManager am = context.getAssets();//context being the activity which called this class.

edited Aug 11 '11 at 13:00

answered Aug 11 '11 at 11:34

Did you keep "extends activity"? Did you get rid of your constructor? How are you calling this class? By an intent? – Aug 11 '11 at 11:40
I call it like this : imageLoader=new ImageLoader(activity.getApplicationContext()); – hardartcore Aug 11 '11 at 11:46
In imageloader use AssetManager is = context.getAssets(); – Aug 11 '11 at 11:50

score 0 · Answer 2 · answered Aug 11 '11 at 11:41

0

If the first class is not really an activity, doen't extend activity just to use this.getAssets(), pass the context (i.e. your activity) when instantiating the class, and use this instance to call getAssets()

answered Aug 11 '11 at 11:41

MByD

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I didn't get what you mean at all..Yes,the ImageLoader class is not an activity.The problem I guess is in calling this.getAssets(); I tried with changing getBitmap method like getBitmap(Context contect,String src) and change AssetManager to context.getAssets(); but it's still wasn't working – hardartcore Aug 11 '11 at 11:45
Get rid of extends Activity. and put AssetManager is = context.getAssets() – Aug 11 '11 at 11:48
I did it and I still got the Exception + 2 more exceptions about cipherinputstream and bufferedinputstream. – hardartcore Aug 11 '11 at 11:59

Android NullPointerException CipherInputStream to Bitmap

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